I guess it is simplifying the expression:

Answer
D or the fourth one because i took the quiz and got it right
First, convert the distance of a typical marathon to kilometers.
1 mi = 1.609 km
26.2 miles = 42.165 km
Divide this distance by Allan's average speed to get his average time.
42.165 km / 12 km/hr = 3.514 hours